Conventionally, wash-down flush toilets have been known as toilets which do not create a siphon effect. Compared to siphon-type flush toilets which discharge waste by the siphon effect, such conventional wash-down flush toilets push waste out by the water flow effect caused by a water drop, and therefore have a simple structure, are low in cost, and do not create a siphon effect, thereby yielding the advantage that the flush water volume used by the flush toilet can be kept low. The wash-down type of flush toilet also conforms to the long standing requirement to conserve water in toilets.
For example, a discharge socket connecting the discharge path of a wash-down flush toilet main body and an under-floor discharge pipe is known (see patent literature 1). The discharge socket has a toilet main body-side connecting member connected to the outlet portion on the discharge path of a toilet main body; an under-floor-side connecting pipe member connected to an under-floor discharge pipe inlet portion and a bent conduit, and an intermediate pipe member extending in essentially a straight line connecting a toilet main body-side connecting pipe member and an under-floor-side connecting pipe member.
In the discharge socket shown in patent literature 1, when discharge water seals the discharge socket bent conduit interior produces a siphon effect, a negative pressure is created which seeks to pull upstream side discharge water into the downstream side, therefore to prevent this, a negative pressure constraining means is disposed in the bent conduit of the discharge socket.